RESUMEN
Near-field optical microscopy and spectroscopy provide high-resolution imaging below the diffraction limit, crucial in physics, chemistry, and biology for studying molecules, nanoparticles, and viruses. These techniques use a sharp metallic tip of an atomic force microscope (AFM) to enhance incoming and scattered light by excited near-fields at the tip apex, leading to high sensitivity and a spatial resolution of a few nanometers. However, this restricts the near-field orientation to out-of-plane polarization, limiting optical polarization choices. We introduce double tips that offer in-plane polarization for enhanced imaging and spectroscopy. These double tips provide superior enhancement over single tips, although with a slightly lower spatial resolution (â¼30 nm). They enable advanced studies of nanotubes, graphene defects, and transition metal dichalcogenides, benefiting from polarization control. The double tips allow varied polarization in tip-enhanced Raman scattering and selective excitation of transverse-electric and -magnetic polaritons, expanding the range of nanoscale samples that can be studied.
RESUMEN
Direct electron beam writing is a powerful tool for fabricating complex nanostructures in a single step. The electron beam locally cleaves the molecules of an adsorbed gaseous precursor to form a deposit, similar to 3D printing but without the need for a resist or development step. Here, we employ for the first time a silver ß-diketonate precursor for focused electron beam-induced deposition (FEBID). The used compound (hfac)AgPMe3 operates at an evaporation temperature of 70-80 °C and is compatible with commercially available gas injection systems used in any standard scanning electron microscope. Growth of smooth 3D geometries could be demonstrated for tightly focused electron beams, albeit with low silver content in the deposit volume. The electron beam-induced deposition proved sensitive to the irradiation conditions, leading to varying compositions of the deposit and internal inhomogeneities such as the formation of a layered structure consisting of a pure silver layer at the interface to the substrate covered by a deposit layer with low silver content. Imaging after the deposition process revealed morphological changes such as the growth of silver particles on the surface. While these effects complicate the application for 3D printing, the unique deposit structure with a thin, compact silver film beneath the deposit body is interesting from a fundamental point of view and may offer additional opportunities for applications.
RESUMEN
Chemical vapor deposition (CVD) is an established method for producing high-purity thin films, but it typically necessitates the pre- and post-processing using a mask to produce structures. This study presents a novel maskless patterning technique that enables area-selective CVD of gold. A focused electron beam is used to decompose the metal-organic precursor Au(acac)Me2 locally, thereby creating an autocatalytically active seed layer for subsequent CVD with the same precursor. The procedure can be included in the same CVD process without the need for clean room lithographic processing. Moreover, it operates at low temperatures of 80 °C, over 200 K lower than standard CVD temperatures for this precursor, reducing thermal load on the specimen. Given that electron beam seeding operates on any even moderately conductive surface, the process does not constrain device design. This is demonstrated by the example of vertical nanostructures with high aspect ratios of ≈40:1 and more. Written using a focused electron beam and the same precursor, these nanopillars exhibit catalytically active nuclei on their surface. Furthermore, by using the onset of the autocatalytic CVD growth, for the first time the local temperature increase caused by the writing of nanostructures with an electron beam can be precisely determined.